Radio frequency identification (RFID) tags are small electronic devices capable of storing data. RFID tags may be active, in which case the tag includes a battery or other power source, or passive, in which case the tag does not include any internal power source. An active RFID tag broadcasts its stored information using its internal power, and an RFID reader may detect the information broadcasted by the active RFID tag. To read a passive RFID tag, however, a reader must first supply the RFID tag with power.
More specifically, to read a passive RFID tag, an RFID reader interrogates the RFID tag to provide power to the tag. Once powered, the RFID tag may transmit the stored data to the RFID reader. By way of example, the RFID tag may store a Universal Identification (UID) that uniquely identifies the RFID tag. Various collections of UIDs have been developed and standardized, and are particularly useful for consumer product tracking in the supply chain and retail environments. For example, RFID tags are often viewed as a replacement or supplement to conventional techniques for identifying products, such as Universal Product Code (UPC) bar codes.
The RFID reader may interrogate the RFID tag to obtain the UID and can associate the UID with a particular item to which the RFID tag is attached. Generally, the RFID tag is affixed to the product, like an ordinary label, in order to identify the product. However, manufacturers may also integrate the RFID tag directly into the product packaging material. In addition, RFID tags have been used to collectively identify a set of identical items, such as a pallet of identical products.
The RFID reader typically comprises an RF module attached to an antenna for powering the RFID tag. The RF module induces a current in the antenna to produce an electromagnetic field, which can interrogate the RFID tag. The RFID tag includes an antenna to capture the electromagnetic field from the RFID reader, an energy storage device (such as a capacitor) to store energy from the captured field, and an integrated controller that contains logic to broadcast the UID. Once the electromagnetic field is brought within range of the RFID tag antenna, the electromagnetic field induces a current in the antenna of the RFID tag, thereby charging the energy storage device of the RFID tag. The charged energy storage device acts as a short-term passive power source to provide power to the integrated controller of the RFID tag. Once powered, the integrated controller broadcasts the UID to the RFID reader via the antenna of the RFID tag, typically by modulating circuit parameters. The RFID reader receives a modulated electromagnetic field from the RFID tag and decodes the received signal to determine the UID. In addition, the RFID reader may compare the UID to a database in order to determine the product associated with the UID.